Cathode ray tube simultaneously generating a plurality of shaped electron beams



May 7, 1968 c. R. CORPEW 3,382,392

CATHODE RAY TUBE SIMULTANEOUSLY GENERATING A PLURALITY OF SHAPEDELECTRON BEAMS Filed Jan. 16, 1967 \k INVENTOIZ "N CHAEL5 205527 605 BYcgda/Aanjdi4%fi fim iz ATTORNEYS United States Patent 3,382,392 CATHODERAY TUBE SIMULTANEOUSLY GENERATING A PLURALITY OF SHAPED ELECTRON BEAMSCharles Robert Corpew, La Mesa, Califl, assignor to Stromberg-CarlsonCorporation, Rochester, N.Y., a corporation of Delaware Filed Jan. 16,1967, Ser. No. 609,444 6 Claims. (Cl. 313-69) ABSTRACT OF THE DISCLOSUREA shaped beam tube in which an electron beam is divided into a pluralityof separate electron beams and the separate electron beams are thenpassed through a means for forming a cross section of each beam. Theshaped beams are then directed and focused so as to impinge on a screento thereby produce displays corresponding to the cross sections of thebeams.

This invention relates to shaped beam tubes such as are used to store ordisplay characters or similar information. More particularly, theinvention relates to an improved shaped beam tube and to a means andmethod for producing a plurality of shaped electron beams therein.

A shaped beam tube is a cathode ray tube wherein an electron beam isshaped as it passes from an electron gun to a phosphor coated screensuch that the cross section of the beam is of a pro-selectedconfiguration. The area of the screen energized by impingement of thebeam thereon, therefore corresponds in shape to the shaped cross sectionof the beam. Shaped beam tubes of this type are manufactured and sold byStromberg-Carlson Corporation under the registered trademark Charactron.

Normally, in such shaped beam tubes the electron beam is shaped bypassing the same through a selected one of a series of stencil-likeapertures in an electron opaque plate. The stencil-like aperturescorrespond to characters, such as letters of the alphabet. A number ofcharacters are shaped such that an island is formed by the apertureforming the character. To retain such islands in position bridges areprovided, which bridges cause discontinuities in the charactersdisplayed on the screen. These discontinuities may be aestheticallyobjectionable and preclude certain characters, such as Chinesecharacters from being displayed.

It is sometimes preferred to utilize a shaped beam tube having severalelectron beams in order to increase the brightness of the datadisplayed, the quantity of data displayed, or the repetition rate. Insuch a tube, the positional relationship of the energized areas on thescreen is affected by the positional relationship between the sources ofeach of the separate electron beams. Where each electron beam isproduced by a separate electron gun, variation in the relativepositional relationships of the guns may occur due to thermal expansionand contraction of structural elements, or may occur as a result ofoutside vibration and shock. Moreover, during assembly, the precision ofmechanical adjustment of the position of several electron guns may belimited.

Although tolerable for some types of displays, variation and limitedprecision in the relative positional relationship of several electronguns may be intolerable where the positional relationship between twoenergized areas on the target screen is critical to the quality of theresultant display. For example, the accuracy of a map or graph, or thequality of a character, depends on an accurate relationship between thevarious lines of which it is composed. If different portions of acharacter or different line segments in a graph or map are produced byseparate "ice electron beams, display quality may be severely impaireddue to the aforementioned variation or limited precision in the relativeposition of several independent electron beam sources. Moreover, the useof an independent source for each of several electron beams may render atube too expensive or complex for some purposes.

It is an object of this invention to provide an improved shaped beamtube. Another object is the provision of a means for producing aplurality of shaped electron beams in a shaped beam tube. Still anotherobject is to provide a shaped beam tube which is capable of producingcomplex images of a high quality. A further object is to provide ashaped beam tube utilizing a plurality of electron beams which are notsusceptible to excessive variation in positional relationship at theirsource. A more specific object is to provide an improved shaped beamtube using an apertured electron-opaque plate, and which is capable ofproducing high quality images of items, such as certain alphanumericcharacters, without the necessity for bridge support in the plate. Astill further object is to provide a shaped beam tube, utilizing aplurality of electron beams, which is low in cost and of relativelysimple construction.

Other objects of the invention will become apparent to those skilled inthe art from the following description taken in connection with theaccompanying drawing wherein:

FIGURE 1 is a perspective schematic view of a shaped beam tubeconstructed in accordance with the invention;

FIGURE 2 is a plan view of a portion of an apertured plate of a typewhich has been previously employed in a shaped beam tube; and

FIGURE 3 is a composite view of two apertured plates used in oneembodiment of the tube shown in FIGURE 1.

Very generally, the shaped beam tube comprises an elongated, evacuatedenvelope 5, which includes at one end thereof an electron gun 7 forproducing a beam 9 of electrons and, at the other end thereof, anenergizable target screen 11. The electron beam produced by the electrongun is divided into a plurality of separate electron beams 13, 15, 17and 19 by means 21. The separate electron beams are passed through abeam shaping means 23 for forming the cross section of each beam into apreselected shape. The shaped beams are then directed and focused by ameans 24 and impinge on the screen 11 to thereby produce displayscorresponding to the cross sections of the beams.

Referring now more particularly to FIGURE 1, the various elements of theshaped beam tube are shown contained within the elongated evacuatedenvelope 5 indicated by the dashed lines. The electron gun 7 forproducing the beam of electrons, indicated at 9 is disposed at one endof the envelope 5. The electron gun may be of any suitable construction,and appropriate provision is provided for electrical connection, notillustrated, to provide proper potentials for the various parts of theelectron gun. For example, the electron gun may comprise an emissivecathode which is heated to produce emission of electrons. Such electronsare accelerated and focused into the beam 9, which is diverging andrelatively large in cross section, by suitable electrodes (not shown).

The electron beam 9 produced by the gun is divided into four separateelectron beams 13, 15, 17 and 19 by the dividing means 21. In theillustrated embodiment, the dividing means comprises an electron opaqueplate having four apertures 25, 27, 29 and 31 therein.

Selecting means 33 are included in the envelope '5 for directing thefour electron beams so that each impinges on a selected portion of theapertured plate or beam shaping member 23 described hereinafter. Theselecting means 33 include four sets 35, 37, 39 and 41 of deflectingplates, one set for each beam. Each of the sets of plates includes apair 3 of parallel plates for vertical deflection of the associatedelectron beam and a pair of parallel plates for horizontal deflection ofthe associated electron beam. Suitable electrical connections, notillustrated, are made to the plates in each set for establishingpotentials thereacross to accomplish a desired beam deflection.

Variation of the potential across the pairs of plates in each of thesets 35, 37, 39 and 41 causes deflection of the associated electron beam13, 15, 17 or 19 to thereby select one portion of the beam shaping means23. The beam shaping means includes four matrices or members 43, 45, 47and 49, one member being provided for each beam. Preferably all fourmatrices are etched or formed from a single sheet of metal. Each beamshaping member includes a plurality of apertures 51 arranged in rows andcolumns. Each aperture 51 forms the beam passing therethrough int-o itsshape, the shape depending upon the desired reproduction upon the screen11, and each may comprise all or part of an alphanumeric character, orother representation such as a spaced segment of the lines of graph ormap. In any event, the potential across the plates in the respectivesets 35, 37, 39 and 41 in the selection assembly 33 is controlled toselect a desired aperture with each beam. In this connection, a DCcentering voltage is applied to each set of plates to direct theassociated beam at the center of the matrix 43, 45, 47 or 49, and avariable voltage is applied to select the proper row or column in thematrix.

Each shaped beam is then converged toward a point on the opposite sideof the envelope axis from the associated set of selection plates 35, 37,39 and 41 by an electron lens 53 positioned between the shaping means 23and the screen 11. The lens 53 may be electrostatic or electromagneticand is illustrated as being a tube disposed within the envelope 5.

Disposed at the points whereat the shaped beams are directed is areference assembly 55 which deflects the beams so that the four beamsare closely spaced and lie in a plane which extends parallel to the axisof the envelope 5. The illustrated reference assembly 55 comprises foursets 57, 59, 61 and 63 of deflection plates, each set including a pairof parallel plates for vertical deflection and a pair of parallel platesfor horizontal deflection. The shaped electron beams 13, 15, 17 and 19pass through the respective sets of plates to be deflected thereby. Toobtain the required deflection of the beams, a signal composed of threecomponents is applied to each set of plates. First, a variable signal isapplied to cancel the component of electron velocity extendingperpendicular to the axis of the envelope which was caused by thevariable voltages applied to the associate set of selecting plates 35,37, 39 and 41. The second component is a fixed DC signal which causesthe four separate beams to bend so as to intersect at a common point onthe screen 11. In the alternative, this second component may be replacedby the action of a convergence lens. The third component is a minorpositioning signal which causes the beams to be slightly displaced fromeach other in the same plane. This positioning signal may be a fixed DCvoltage or a voltage controlled by computer signals.

After the reference assembly 55 has established the relative positionbetween the shaped beams 13, 15, 17 and 19, the beams pass through adeflection means 65. The deflection means, which may be a yokepositioned within the envelope 55 as shown, or may surround the outsideof the tube envelope, operates in accordance with known principles todeflect the group of electron beams passing therethrough to any desiredarea on the target screen 11. Since the beams passing through thedeflection means 65 are off center, the deflection means 65 ispreferably constructed to provide a uniform field.

The target screen 11 may be of any type suitable to the particularapplication of the shaped beam tube. The screen may, for example,comprise a device for producing a visible display for observation or forphotographic recording, or may comprise part of electronic printingapparatus. The surface of the screen may be coated with a material whichis energizable in response to electron bombardment. Such a screen may,in the case of a direct viewing screen, be comprised of a suitablephosphor which emits light in response to electron bombardment.

In reviewing the operation of the device, the electron gun 7 produces aprimary electron beam 9 which is divided by the apertured plate 21 intoa plurality of secondary electron beams 13, 15, 17 and 19. These beamsare then each passed through a respective one of the apertures 51 in arespective matrix 43, 45, 47 or 49 in the plate 23. The aperture of eachmatrix which is used is selected by the selection assembly 33. The beamsshaped by the apertures 51 are then converged by the lens 53 and arelative position therebetween is established by the reference assembly55. The relative position of the beams thus being established, thedeflection yoke deflects all of the beams to a desired position on thescreen 11. Each beam thereby impinges upon a shaped area of the screenin accordance with the cross sectional shape of the beam.

The shaped beam tube may be employed, for example, to display atypewriter format. The first four letters are unblanlred simultaneously,adjacent one another. Then new selector signals are applied, and theposition set by the deflection means is stepped four positions to theright, as viewed from the front of the screen, and the next fourcharacters are unblanked. This operation is continued horizontallyacross the screen and then the beams are stepped down one position and asecond line of characters is started.

By producing a plurality of electron beams from a single beam generatedat a single source, rather than producing each beam at an independentsource, the beams suffer common position deflection. With separate andindependent sources, thermal expansion or outside shock may result in avariation of the relative position between the beams. To compensate forsuch change in relative position electronically, even if possible, mayresult in undue complexity in electronic circuitry and problems of delayin sensing and correcting such errors.

The above described construction also makes it easier to establish adesired positional relation, between the sources of the beams, duringassembly than is possible with separate electron guns. In the lattercase, mounting structure is often subject to tolerance variation andassembly difficulties that affect the relative gun position. Thedescribed construction avoids such variation and difiiculties since therelative beam source position is established by the apertures 25, 27, 29and 31 when the plate 21 is fabricated. As a practical matter, closetolerances are usually easier to hold during fabrication of one part,rather than in the assembly of many parts.

The foregoing described attributes of the present invention haveparticular advantage in producing a high quality accurate image upon thetarget screen 11 where the relative position of the energized areasproduced by respective beams is critical. For example, the shaped beamtube may be employed to form characters which do not include the bridgesinherent in previously available shaped beam tubes. Referringparticularly to FIG- URE 2, a portion of a prior art matrix or electronopaque plate 67 having an aperture 69 therein for shaping the beam in amanner to produce the letter O is shown. Naturally, to maintain thedesired shape for the aperture 69, the opaque center 71 of the letter 0must be suitably supported. To this end, a pair of bridges 73 and 75 areprovided. For high quality printing or visible reproduction, it isdesirable to avoid such bridges. Moreover, where complex characters areto be reproduced, such as Chinese characters, extensive bridging mayconfuse and obscure the character being reproduced.

The foregoing problems may be avoided by utilizing half of the letter O.The two electron beams 13 and 15 I passing through the respectiveapertures are positioned relative to each other by the referenceassembly 55 so that, when they impinge upon the target screen, the endsof the arcuate segments of the letter will exactly meet. This produces aletter O which is free from bridges. The same principle may be appliedto reproducing other characters without the use of bridges. Theinvention is of particular advantage in such a technique in thatrelative displacement between the two or more electron beams used doesnot occur, due to their origin in a common beam and their division by asingle apertured plate.

Alternately, one aperture of the pair forming a character may be shapedlike that shown in FIGURE 2, and the other aperture may be shaped topass a beam corresponding to the shape of the bridges. In other words,the apertures are provided in complementary pairs. The beams are thensuperimposed on the screen 11 by omit ting the third component (theminor positioning signal) of the signal applied to the referenceassembly 55.

It may therefore be seen that the invention provides an improved shapedbeam tube and a means producing a plurality of shaped electron beamstherein. Excessive change in the relative position of the sources of theelectron beams does not occur, thereby enabling the production ofsuperior quality images on a display screen. This is because therelative position of energized areas on the display screen produced bytwo or more electron beams is not subject to excessive variation due torelative variation in the source of the beams. The invention therebyfacilitates the reproduction of complex characters comprised of segmentsproduced by separate electron beams. A particular advantage of theinvention is that, in the reproduction of many types of characters,bridging may be avoided. Moreover, only a single electron gun isnecessary, effecting a substantial cost reduction over a tube utilizingseveral electron guns and suitable mounting structure therefor.

Various embodiments of the invention in addition to that shown anddescribed herein will become apparent to those skilled in the art fromthe foregoing description and accompanying drawings. Such otherembodiments and modifications thereof, are intended to fall within thescope of the appended claims.

What is claimed is:

1. In a shaped beam tube, means for producing a plurality of shapedelectron beams comprising, means for producing a primary electron beamfrom a single source of electrons, means for dividing said primaryelectron beam into a plurality of secondary electron beams, beam 6shaping means having a plurality of beam shaping apertures, and meansfor individually deflecting each of said secondary electron beams topass through selected ones of said beam shaping apertures.

2. A shaped beam tube comprising, an electron gun for producing aprimary beam of electrons, a target screen, means positioned betweensaid electron gun and said target screen for dividing the primaryelectron beam produced by said electron gun into a plurality ofsecondary electron beams, beam shaping means positioned between saiddividing means and said screen for forming the cross section of each ofsaid secondary electron beams into predetermined shapes, and means fordirecting and focusing the plurality of secondary electron beams toimpinge upon areas of said screen, each area corresponding in shape tothe cross sectional shape of the associated electron beam.

3. A tube in accordance with claim 2 wherein said dividing meanscomprise an electron-opaque plate having a plurality of electronapertures therein.

4. A tube in accordance with claim 3 wherein said beam shaping meanscomprises a second electron opaque plate having a plurality of matricesof electron apertures therein of predetermined shape, said matricescorresponding in number to the number of electron apertures in saidfirst electron opaque plate.

5. A tube in accordance with claim 2 wherein said directing and focusingmeans include a plurality of first deflection means, one for each of theplurality of electron beams, said first deflection means beingpositioned between said dividing means and said shaping means, aplurality of second deflection means, one for each of the plurality ofelectron beams, said second deflection means being positioned betweensaid shaping means and said screen, and an electron lens positionedbetween said shaping means and said second deflection means for focusingsaid secondary beams at said second deflection means.

6. A tube in accordance with claim 4 wherein at least two of thematrices have complementary apertures and directing and focusing meansappropriately positioning the secondary beams passing through saidcomplementary apertures so as to form complete characters.

References Cited UNITED STATES PATENTS 2,495,738 1/ 1950 Labin et al.313--77 X 2,943,220 6/1960 McNaney 313--86 2,978,608 4/ 1961 Gaifney313-87 X 2,981,861 4/1961 Dawirs 3158.5 3,327,149 6/1967 Corpew 313--86JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner.

